| Alexion Pharmaceuticals | business, enterprise, public company | Cheshire | 1992 |
| Allegheny College | Colleges That Change Lives, private not-for-profit educational institution, liberal arts college in the United States | — | April 1815 |
| AllianceBernstein | business, enterprise, public company | Nashville | 1967 |
| Alliant University | private for-profit educational institution, university | San Diego | 2001 |
| Allis-Chalmers | business | Milwaukee | 1901 |
| Allison Engine Company | business | Indianapolis | 1915 |
| Aloha Air Cargo | airline | Honolulu | 2008 |
| Aloha Airlines | airline | Honolulu | 1946 |
| Altair Engineering | business, public company | Troy | 1985 |
| Altria | multinational corporation, public company | Richmond | 1985 |
| Amaze Entertainment | video game developer, business | Kirkland | 1997 |
| Amazon | very large online platform, business, enterprise, public company | Seattle | July 5, 1994 |
| Amazon Air | virtual airline | — | November 1, 2015 |
| Amazon Go | retail chain | Seattle | December 5, 2016 |
| Amazon Lab126 | business | Cupertino | 2004 |
| Amazon MGM Studios | film production company, film distributor | Culver City | 2010 |
| Amazon Robotics | business | Massachusetts | January 1, 2003 |
| Amblin Entertainment | television production company, animation studio, film production company | Universal City | 1981 |
| Amblin Partners | joint venture, company | Universal City | December 16, 2015 |
| Amblin Television | business | Universal City | July 31, 1984 |
| Ameren | holding company, public company | St. Louis | 1997 |
| America West Airlines | airline | Tempe | 1981 |
| American Academy in Rome | nonprofit organization, educational institution, research center | Rome, New York City | 1894 |
| American Academy of Arts and Sciences | nonprofit organization, learned society, academic publisher | Cambridge | May 4, 1780 |
| American Academy of Dramatic Arts | academy, drama school, private not-for-profit educational institution, organization | New York City | 1884 |
| American Antiquarian Society | research library, nonprofit organization, historical society, learned society | Worcester | 1812 |
| American Association for the Advancement of Science | nonprofit organization, open-access publisher, international organization, academic publisher | Washington, D.C. | September 20, 1848 |
| American Association of Physics Teachers | publishing house, scientific society | — | December 31, 1930 |
| American Automobile Association | nonprofit organization, business | Heathrow | 1902 |
| American Axle | business, enterprise, public company | Detroit | 1994 |
| American Bible Society | Bible society, nonprofit organization | Philadelphia | May 11, 1816 |
| American Bridge Company | business | Coraopolis | 1900 |
| American Cyanamid | business | Wayne | 1907 |
| American Economic Association | organization, open-access publisher, scientific society | Nashville | 1885 |
| American Electric Power | holding company, business, enterprise, public company | Columbus, Jersey City | August 1927 |
| American Express | multinational corporation, business, card association, public company | New York City | 1850 |
| American Geographical Society | publishing house, geographical society | Manhattan | 1851 |
| American Heart Association | nonprofit organization, medical organization, open-access publisher | Dallas | June 10, 1924 |
| American Hockey League | professional sports league | — | 1936 |
| American Institute of Physics | nonprofit organization, archives, publishing house, open-access publisher, scientific society | College Park | 1931 |
| American International Group | business, enterprise, public company | New York City | 1919 |
| American Library Association | nonprofit organization, open-access publisher, professional association, library association, academic publisher | Chicago | October 6, 1876 |
| American Line | transport company | Philadelphia | 1871 |
| American Locomotive Company | business | Schenectady, New York City | June 24, 1901 |
| American Motors Corporation | automobile manufacturer | Kenosha | 1954 |
| American Psychological Association | regulatory college, nonprofit organization, publishing house, open-access publisher, professional association, school accreditor | Washington, D.C. | July 1892 |
| American Sociological Association | nonprofit organization, learned society, academic publisher | 1430 K Street | 1905 |
| American Statistical Association | production company, nonprofit organization, open-access publisher, scientific society | Boston | November 27, 1839 |